Lytic polysaccharide monooxygenases from Myceliophthora thermophila C1 differ in substrate preference and reducing agent specificity

Table 2 Overview of electron donor specificity of MtLPMO9A, MtLPMO9B or MtLPMO9C

Group	No.	Reducing agent	MtLPMO9A				MtLPMO9B			MtLPMO9C
			Activity compared to ascorbic acid %
			C1-/C4-ox and non-ox	C1-ox	C4-ox	Non-ox	C1-/C4-ox and non-ox	C1-ox	Non-ox	C1-/C4-ox and non-ox	C4-ox	Non-ox
I	1	3-Hydroxy-4-methoxycinnamic acid	0	0	0	0	0	0	0	0	0	0
	2	Homovanillic acid	0	0	0	0	0	0	0	0	0	0
	3	Naringin	0	0	0	0	0	0	0	0	0	0
	4	p-coumaric acid	0	0	0	0	0	0	0	0	0	0
	5	Sinapic acid	23	23	31	24	4	3	14	15	12	18
	6	Syringic acid	0	0	0	0	0	0	0	0	0	0
	7	Vanillic acid	0	0	0	0	0	0	0	0	0	0
II	8	(−)-Epicatechin	77	68	90	27	21	19	34	21	15	26
	9	(+)-Catechin	43	47	41	24	7	6	17	6	5	7
	10	3,4-Dihydroxybenzaldehyde	9	13	7	0	0	0	0	0	0	0
	11	3,4-Dihydroxybenzoic acid	13	15	13	0	1	1	2	4	5	3
	12	3,4-Dihydroxycinnamic acid	0	0	0	0	49	48	63	0	0	0
	13	3,4-Dihydroxyphenylacetic acid	92	79	105	68	18	17	31	12	9	14
	14	3-Methylcatechol	102	87	121	49	22	20	38	14	15	12
	15	4-Chlorocatechol	72	68	75	74	8	7	24	24	21	26
	16	Caffeic acid	49	49	52	20	8	7	26	0	0	0
	17	Carminic acid	8	7	8	21	0	0	0	3	2	4
	18	Catechol	65	57	75	26	8	7	18	11	12	10
	19	Chlorogenic acid	36	38	36	25	4	3	18	0	0	0
	20	Dopamine hydrochloride	93	71	105	132	46	45	57	6	2	10
	21	l -3,4-Dihydroxyphenylalanine	101	75	123	86	79	78	84	33	26	41
	22	Quercetin	0	0	0	0	0	0	0	0	0	0
	23	Taxifolin	0	0	0	0	15	15	20	4	3	4
	24	Resorcinol	0	0	0	0	0	0	0	0	0	0
	25	Hydroquinone	51	55	51	25	2	1	10	5	4	7
III	26	Gallic acid	81	72	94	38	46	45	54	22	18	26
	27	(−)-Epigallocatechin-gallate	76	56	97	30	79	79	83	11	9	12
	28	Tannic acid	0	0	0	0	18	13	66	0	0	0
IV	29	Reduced glutathione	0	0	0	0	16	15	30	8	7	8
	30	l -cysteine	16	23	13	0	22	20	40	6	7	4
	31	Allyl iso-thiocyanate	0	0	0	0	0	0	0	0	0	0
	32	d-methionine	0	0	0	0	0	0	0	0	0	0
V	33	Ascorbic acid	100	100	100	100	100	100	100	100	100	100
		Peak area (nC x min)^a	(0.897)	(0.460)	(0.058)	(0.360)	(3.273)	(2.962)	(0.311)	(1.542)	(0.760)	(0.781)
	34	d-quinic acid	0	0	0	0	0	0	0	0	0	0

The total sum of integrated peak areas of released oxidized (C1-ox, C4-ox) and non-oxidized (non-ox) and both (ox and non-ox) gluco-oligosaccharides from RAC, incubated with either MtLPMO9A, MtLPMO9B or MtLPMO9C in the presence of ascorbic acid, was taken as a reference and equals to 100 % of the LPMO activity. The numbers correspond to the relative activity of MtLPMO9A, MtLPMO9B or MtLPMO9C compared to ascorbic acid (total sum integrated peak areas of released oxidized and non-oxidized gluco-oligosaccharides of a reducing agent compared to ascorbic acid (areas from Fig. 5). Auto-oxidation of RAC was absent for all reducing agents tested based on the absence of oxidized or non-oxidized gluco-oligosaccharides. Reducing agents that can donate electrons to all three LPMOs are highlighted in italics. See “Methods” for details about the activity assays
^aIntegrated peak areas of released C1-, C4-oxidized and non-oxidized gluco-oligosaccharides after incubation of MtLPMO9A, MtLPMO9B and MtLPMO9C with RAC in the presence of 1 mM ascorbic acid based on HPAEC (Fig. 5)

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